Hydroxyapatite has a chemical structure in which calcium ions and phosphate groups are regularly arranged in a high density state. Such hydroxyapatite serves as an amphoteric ion exchange body and has adsorption capability due to electrostatic interaction by the amphoteric ion exchange body.
Therefore, powder (hydroxyapatite powder) constituted of this hydroxyapatite is widely used as an adsorbent which is used for a column of separating biologically-relevant materials such as proteins, nucleotides, nucleic acids, cells, and the like (U.S. Pat. No. 7,150,862 B2 is an example of the related art).
More specifically, in a case where a protein is separated from a sample containing proteins, the hydroxyapatite powder is widely used as an adsorbent which is used for a column of separating the biologically-relevant materials (proteins). If the protein is an acid protein, carboxyl groups included in a chemical structure of the acid protein make coordinate bonds with the calcium ions of the hydroxyapatite powder, thereby adsorbing the acid protein by the hydroxyapatite powder. Further, if the protein is a basic protein, amino groups contained in a chemical structure of the basic protein make ion bonds with the phosphate groups of the hydroxyapatite powder, thereby adsorbing the basic protein by the hydroxyapatite powder. Therefore, the protein is separated from the sample containing the proteins due to differences among adsorption capabilities of the proteins with respect to the hydroxylapatite powder.
In separation columns including such hydroxyapatite powder as an adsorbent (that is, an adsorption apparatus), recently, not only a separation column for industrial use but also a separation column for research and development use tend to become large in size. This tendency results in increase of a pressure applied to the hydroxyapatite powder which has been filled into the separation column as the adsorbent. By increasing such a pressure applied to the adsorbent (hydroxyapatite powder), the adsorbent is crushed when the adsorbent is filled into the separation column or the separation column is being used actually. As a result, a filter provided in one end of the separation column is cologged with the crushed adsorbent. Therefore, there is a problem in that frequent exchange of the adsorbent is needed.
In order to solve such a problem, recently, attention has been paid to powder (fluoroapatite powder) constituted of fluoroapatite which is produced by substituting at least a part of hydroxyl groups of hydroxyapatite by fluorine atoms (JP-A 2004-330113 is an example of the related art).
This fluoroapatite has substantially the same crystal (chemical) structure as that of hydroxyapatite, and therefore has substantially the same adsorption characteristics (adsorption capability) to the biologically-relevant materials such as proteins and the like as those of hydroxyapatite. Further, the fluoroapatite powder is a more stable material as compared with the hydroxyapatite powder. Therefore, since the fluoroapatite powder has properties such as improved particle strength and high acid resistance, attention has also been paid to the fluoroapatite powder.
However, even if the fluoroapatite powder is used as an adsorbent for a separation column, in a case where the separation column is used as a column for industrial use which is large in size, it cannot be said that the fluoroapatite powder has sufficient particle strength to be required to the adsorbent.